The European Union is expected to seek around €10bn from the UK – even if a no-deal Brexit goes ahead on April 12, it has been reported.
Sources reportedly said that the fee Britain will have to hand over to the EU in contributions for existing obligations.
In exchange, UK beneficiaries of EU funding would continue to receive grants for the rest of the year.
The news comes as MPs are braced for yet another round of voting in the House of Commons.
A senior EU source told Irish broadcaster RTÉ News: “We hope to have it wrapped up this week.”
The official said there had been “informal” signals from the UK Treasury that Britain would be willing to consider paying the remainder of its budget obligations until the end of the year.
This is in order that universities, local communities and any other beneficiaries would not be frozen out of EU structural, regional development and research funding immediately.
Farmers, including those in Northern Ireland, will continue to receive direct payments in any case as Common Agriculture Policy (CAP) funding has already been committed by the EU for the entirety of 2019.
It would also mean British officials working in EU institutions would continue to have their pensions paid.
However, on March 13 the House of Commons European Scrutiny Committee raised serious concerns about the idea and sharply criticised what it called “ambiguous” responses from the Treasury on the issue.
The UK’s gross budget contribution to the EU for 2019 is €17.49bn.
Of that sum, Britain has already contributed €7.2bn, meaning that in a no-deal situation the EU would face a shortfall of €10.2bn this financial year.
The EU now expects that amount to be paid.
A Downing Street spokesman said: “We’ve said before that if we leave without a deal, the financial settlement as set out in the Withdrawal Agreement will no longer apply.
“This remains our position but, of course, we are a country that honours our obligations, and those would need to be resolved.”
In 2017, the UK received back an estimated €4.6bn in EU funding, as well as the rebate of €6.5bn.
The new EU law, to be adopted this week, was first tabled by the European Commission in January as part of the intensification of its no-deal planning.
On Tuesday senior cabinet ministers will meet for five hours – the first three will be in a “political” session in the absence of civil servants – to discuss the way ahead, amid speculation about possible resignations, a general election or change of Tory leader.
Despite seeing her deal again defeated on Friday, the Prime Minister is determined to bring it back to the Commons for a fourth time in a final roll of the dice to get it over the line before the EU deadline of April 12.